Fan foundation pile foundation construction method

Abstract

The invention relates to the technical field of fan foundations, and provides a fan foundation pile foundation construction method which comprises the following steps that a cement soil mixing pile is constructed in the center of a prestressed pipe pile, and the diameter of the cement soil mixing pile is larger than that of the prestressed pipe pile; during construction of the cement-soil mixing pile, thin slurry is sprayed during downward drilling for the first time, thick slurry is synchronously sprayed during drilling lifting, the repeated stirring frequency is not less than 2 times, and the cement-soil mixing pile with the pile bottom elevation not higher than the designed bottom elevation of the prestressed pipe pile is formed; before the cement soil mixing piles are solidified, the prestressed pipe piles are pressed into the designed depth; the pile sinking problem in high underground water and dense sandy soil geology can be solved, the physical and mechanical properties of soil around the pile are effectively improved by constructing the cement soil mixing pile with the larger diameter in the center of the prestressed pipe pile, the problem that pile sinking cannot be achieved under the dense sandy soil geology condition can be effectively solved, and the pile sinking method is suitable for various soil layers and hard soil layers containing dense sandy soil and the like; and the application range of the prestressed pipe pile is widened.

Description

Technical Field

[0001] The present invention relates to the technical field of wind turbine foundations, and in particular to a wind turbine foundation pile foundation construction method. Background Art

[0002] As the key bearing structure of wind turbine generator sets, wind turbine foundations often need to be constructed under complex geological conditions, especially in areas with high groundwater levels and underlying dense sandy soil. Pile foundation construction faces two technical difficulties: on the one hand, sinking piles under geological conditions with high groundwater levels will cause large excess pore water pressure; on the other hand, the high frictional resistance of dense sandy soil (standard penetration number N ≥ 15) makes it difficult to penetrate traditional pile foundations, and the accumulation of excess pore water pressure during pile sinking may cause the pile body to tilt or the surrounding soil to uplift.

[0003] In the existing technology, the common pile foundations are mainly the following two types: First, cast-in-place piles can be widely used in various foundations. Compared with the hammer method of sinking piles, the construction produces much less noise and vibration, and can produce piles with larger diameters than precast piles. Cast-in-place piles are primarily constructed by pouring concrete into the hole. Concrete quality is difficult to control, and the quality of the construction significantly impacts the pile's bearing capacity. Common construction issues include skewed holes, sand gushing, grout leakage, hole collapse, necking, cage misalignment, conduit blockage, and broken piles.

[0004] 2. Prestressed concrete pipe piles have high single pile bearing capacity, a wide range of design options, low cost, convenient transportation and hoisting, quick pile connection, pile length not limited by construction machinery, fast construction speed, high work efficiency and short construction period. However, prestressed concrete pipe piles are not suitable for use under certain geological conditions, such as soil layers with difficult-to-remove boulders and obstacles; soil layers with hard interlayers that are not suitable as bearing layers and difficult for pipe piles to penetrate; karst strata with no suitable bearing layers on the bedrock surface; non-karst areas where the overburden above the bedrock is soft soil layers such as silt, with moderately or slightly weathered rock layers directly below or only a thin layer of strongly weathered rock on the moderately weathered rock surface; the bearing layer at the pile end is a shallowly buried weathered rock layer that softens easily when exposed to water; and rock and soil layers (including groundwater) that have a strong corrosive effect on the concrete, steel bars and steel components of the pipe piles.

[0005] Comprehensive analysis shows that the core contradictions faced by existing technologies in high groundwater dense sandy soil strata are: Due to the dual effects of high hydrostatic pressure and dense sand, if prefabricated pipe piles are used, the traditional pile sinking method cannot effectively sink the piles and requires drilling. Even if drilling, there is a risk of hole collapse. If cast-in-place piles are used, wall protection is required, which is costly. Summary of the Invention

[0006] The present invention provides a wind turbine foundation pile construction method to solve the defects of the prior art in that the pile sinking resistance in high groundwater dense sandy soil strata is large, the traditional process is high in cost and the quality is unstable, and achieve The technical effects include increased pile foundation bearing capacity, shortened construction period and optimized environmental performance.

[0007] The present invention provides a wind turbine foundation pile construction method, comprising the following steps: Constructing a cement-soil mixing pile at the center of the prestressed pipe pile, wherein the diameter of the cement-soil mixing pile is larger than the diameter of the prestressed pipe pile; During the construction of the cement-soil mixing pile, the drill is first lowered and thin slurry is sprayed, and when the drill is lifted, thick slurry is sprayed simultaneously. The mixing is repeated at least twice to form a cement-soil mixing pile with a pile bottom elevation not higher than the designed bottom elevation of the prestressed pipe pile; Before the cement-soil mixing piles solidify, the prestressed pipe piles are pressed into the designed depth.

[0008] According to a wind turbine foundation pile construction method provided by the present invention, pressing the prestressed pipe piles to a designed depth comprises: The prestressed pipe pile is pressed into the cement-soil mixing pile by hammering or static pressure to complete the pile sinking, and the pressing force is not less than the standard value of the vertical ultimate bearing capacity of the prestressed pipe pile.

[0009] According to a wind turbine foundation pile construction method provided by the present invention, the cement-soil mixing pile adopts vertical continuous mixing, the cement content is ≥12%, and the water-cement ratio is 0.5-0.6.

[0010] According to a wind turbine foundation pile construction method provided by the present invention, the cement soil mixing pile and the prestressed pipe pile are arranged concentrically, and the difference between the diameter D1 of the cement soil mixing pile and the diameter D2 of the prestressed pipe pile is between 200-300 mm.

[0011] According to a wind turbine foundation pile construction method provided by the present invention, the cement soil mixing pile forms a whole with the prestressed pipe pile after solidification, and a concrete cushion layer is provided on the top of the cement soil mixing pile.

[0012] According to a wind turbine foundation pile construction method provided by the present invention, the drilling speed is ≤0.8m / min.

[0013] According to a wind turbine foundation pile foundation construction method provided by the present invention, the slurry density of the thin slurry is between 1.2-1.4g / cm³, and the spraying amount accounts for 10%-30% of the total slurry volume; the slurry density of the thick slurry is between 1.5-1.8g / cm³, and the spraying amount accounts for 70%-90% of the total slurry volume.

[0014] According to a wind turbine foundation pile construction method provided by the present invention, the method also includes: performing low-strain, high-strain detection and static load test on the prestressed pipe piles after being pressed in, using low-strain to detect the integrity of the pile body of all piles, and the integrity of the pile body should reach Class I or Class II piles, using high strain to detect the vertical compressive bearing capacity of a single pile, and testing 5 piles at each machine position, and using static load test to detect the pull-out resistance and horizontal bearing capacity of the piles, and the number of static load tests is 3, to ensure that the pile body quality and bearing capacity of the pipe piles meet the design requirements.

[0015] According to a wind turbine foundation pile construction method provided by the present invention, before constructing the cement-soil mixing pile at the center position of the prestressed pipe pile, the method includes: determining the geological conditions of the pile foundation.

[0016] The present invention provides a wind turbine foundation pile construction method. The present invention is an adaptability optimization for geological conditions, and can solve the problem of prestressed pipe pile sinking under high groundwater and dense sandy soil conditions. By constructing a cement-soil mixing pile with a larger diameter in the center of the prestressed pipe pile, the physical and mechanical properties of the soil around the pile are effectively improved, and the side friction resistance during pile sinking is reduced, which can effectively solve the problem of being unable to sink piles under dense sandy soil conditions; avoid the problem of pipe piles being unable to penetrate due to dense sandy soil; and avoid the phenomenon of direct pile sinking in traditional solutions, which is prone to pile body tilting due to excess pore water pressure, or the need to guide a hole but with the risk of hole collapse. The present invention changes the properties of the soil around the pile in advance through the cement-soil mixing pile, which is beneficial to pile foundation sinking and avoids the risk of hole collapse. By spraying thin slurry during the first drilling, the drill rod can be lubricated, the resistance to drilling can be reduced, and the drilling requirements of highly dense sand can be met; when lifting the drill, thick slurry is sprayed and repeatedly stirred to ensure the uniformity of the cement soil, so that the final cement soil mixing pile has no defects such as necking and broken piles, and can block the erosion of groundwater on the pile body, while improving the standard value of pile side friction resistance; moreover, the composite structure formed by the cement soil mixing pile and the prestressed pipe pile can expand the load transfer area through the large pile diameter of the cement soil mixing pile, and provide rigid support through the prestressed pipe pile. The combined effect of the two improves the characteristic value of the bearing capacity of the single pile, meeting the strict requirements of the wind turbine foundation for settlement difference; it is suitable for geological conditions such as liquefied sand, high groundwater, and dense sand layers, and broadens the application range of prestressed pipe piles. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 It is a cross-sectional view of a wind turbine foundation provided by an embodiment of the present invention.

[0019] Figure 2 This is a flow chart of a wind turbine foundation pile foundation construction method provided by an embodiment of the present invention.

[0020] Reference numerals: 1. Prestressed pipe piles; 2. Cement-soil mixing piles; 3. Concrete cushion layer. DETAILED DESCRIPTION

[0021] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0022] The following combination Figure 1-Figure 2 A wind turbine foundation pile construction method according to the present invention is described.

[0023] An embodiment of the present invention provides a wind turbine foundation pile construction method, which is applied to construction conditions of high groundwater and dense sandy soil, and includes the following steps: Step S100: constructing a cement-soil mixing pile 2 at the center of the prestressed pipe pile 1, wherein the diameter of the cement-soil mixing pile 2 is larger than the diameter of the prestressed pipe pile 1; Step S200: During the construction of the cement-soil mixing pile 2, a thin slurry is sprayed when drilling for the first time, and a thick slurry is sprayed when the drill is lifted. The mixing is repeated at least twice to form a cement-soil mixing pile 2 with a pile bottom elevation not higher than the designed bottom elevation of the prestressed pipe pile 1. Step S300: Before the cement-soil mixing pile 2 solidifies, the prestressed pipe pile 1 is pressed into the designed depth.

[0024] It can be seen from the above scheme that the present invention is an adaptive optimization for geological conditions, and can solve the problem of prestressed pipe pile sinking under conditions of high groundwater and dense sandy soil. By constructing a cement-soil mixing pile 2 with a larger diameter in the center of the prestressed pipe pile 1, the physical and mechanical properties of the soil around the pile are effectively improved, and the lateral friction resistance during pile sinking is reduced, which can effectively solve the problem of being unable to sink piles under dense sandy soil conditions; it avoids the problem of pipe piles being unable to penetrate due to dense sandy soil; it also avoids the phenomenon of direct pile sinking in traditional schemes, which is prone to cause the pile body to tilt due to excess pore water pressure, or requires drilling but there is a risk of hole collapse. The present invention changes the properties of the soil around the pile in advance through the cement-soil mixing pile 2, which is beneficial to pile foundation sinking and avoids the risk of hole collapse; through the first drilling and spraying The thin slurry can lubricate the drill rod, reduce the resistance to drilling, and adapt to the drilling needs of highly dense sand and soil; when lifting the drill, spray the thick slurry and repeatedly stir it to ensure the uniformity of the cement soil, so that the final cement soil mixing pile 2 has no defects such as necking and broken piles, and can block the erosion of groundwater on the pile body, while improving the standard value of pile side friction resistance; moreover, the composite structure formed by the cement soil mixing pile 2 and the prestressed pipe pile 1 can expand the load transfer area through the large pile diameter of the cement soil mixing pile 2, and provide rigid support through the prestressed pipe pile 1. The combined effect of the two improves the characteristic value of the single pile bearing capacity, meeting the strict requirements of the wind turbine foundation on settlement difference; it is suitable for geological conditions such as liquefied sand, high groundwater, and dense sand layers, and broadens the application range of the prestressed pipe pile 1.

[0025] In step S100 of this embodiment, the cement-soil mixing pile 2 is concentrically arranged with the prestressed pipe pile 1, and the difference between the diameter D1 of the cement-soil mixing pile 2 and the diameter D2 of the prestressed pipe pile 1 is between 200-300 mm; In this way, the concentric setting ensures that the prestressed pipe pile 1 and the cement-soil mixing pile 2 form a coaxial composite structure. The load acting on the bottom surface of the wind turbine foundation is transferred to the cement-soil mixing pile 2 through the prestressed pipe pile 1, and then evenly dispersed to the surrounding soil, thereby expanding the load transfer area and improving the bearing capacity of a single pile. When the diameter difference is 200-300mm, the thickness of the cement-soil protective layer is 100-150mm, which can not only fully mix the soil around the pile, but also accommodate the compaction deformation of the cement soil during the pile driving process, ensuring sufficient friction resistance on the pile side.

[0026] In this embodiment, in step S300, the prestressed pipe pile 1 is pressed into the designed depth, including: pressing the prestressed pipe pile 1 into the cement-soil mixing pile 2 by hammering or static pressure to complete the pile sinking, and the pressing force is not less than the standard value of the vertical ultimate bearing capacity of the prestressed pipe pile 1.

[0027] Specifically, after the construction of the mixing piles, the hammering method is suitable for penetrating prestressed pipe piles into cement soil. By impacting with a heavy hammer, such as a drop distance of 1.5-2.5m and a frequency of 3-5 times / min, the side friction resistance of the cement soil is broken through. It is especially suitable for the construction of short piles with a length of no more than 15m. The time for pressing a single pile can be controlled within 20-30 minutes. The static pressure method uses a hydraulic system to apply pressure at a uniform speed, with no vibration and low noise. It is suitable for areas with sensitive surrounding environments such as residential areas and pipeline-dense areas. It can be selected according to different geological conditions to improve construction adaptability.

[0028] Alternatively, pile driving can be carried out within 6 hours before the initial setting of the cement soil. At this time, the cement soil is in a plastic state, which can reduce the resistance to pile driving. At the same time, the pressing process of the prestressed pipe pile 1 can produce secondary compaction of the cement soil of the outer cement-soil mixing pile 2. A pressing force of 1.2 times is used to enhance the friction resistance at the interface between the cement soil and the pipe pile, and to increase the pile side friction resistance by 15%-20%. The pile side friction resistance is the main component of the pile foundation bearing capacity. Taking the prestressed pipe pile 1 with a diameter of 500 mm as an example, when the standard value of the pile side friction resistance is increased from 40 kPa in the traditional process to 60 kPa, the bearing capacity contributed by the side friction resistance of a single pile can be increased from 1256 kN to 1885 kN, and the overall bearing capacity is increased by about 50%. Under the same load demand, the cost can be reduced by reducing the pile length, the number of piles or the pile diameter.

[0029] Furthermore, during the pile driving process, the driving force is monitored in real time through a pressure sensor. Based on the driving force and the settlement rate of the pile body, it is determined whether the designed depth has been reached. This can effectively avoid under-pressurized piles and over-pressurized piles, and solve the problem of insufficient bearing capacity caused by stopping piles based on experience in traditional construction, as well as avoid the problem of pile body fracture due to overpressure.

[0030] In this embodiment, the cement-soil mixing pile 2 adopts vertical continuous mixing, the cement content is not less than 12%, and the water-cement ratio is 0.5-0.6.

[0031] Optionally, the present invention utilizes a single-shaft mixer modified from a three-shaft mixer during the vertical continuous mixing process. This allows for wet mixing for dense sandy soils, while dry mixing can be used for soils with high groundwater levels or soft soils. Conventional single-shaft mixers have low power, making cutting difficult in dense sandy soils. Traditional three-shaft mixers, while high-powered, are primarily used for strip foundation reinforcement construction, such as cofferdams and retaining walls, and are unsuitable for single-hole pile construction. Therefore, the present invention allows for the use of a modified single-shaft mixer for cement-soil pile construction.

[0032] Specifically, the vertical continuous mixing process is as follows: when drilling for the first time, spray thin slurry (water-cement ratio 0.8-1.0), and the drill rod cuts into the dense sand at a speed of no more than 1.0m / min. The thin slurry is used to lubricate the drill rod and preliminarily improve the soil at the pile position; when lifting the drill, spray thick slurry (water-cement ratio 0.5-0.6), and stir while lifting the drill at a speed of ≤0.8m / min, completing two mixings; then repeat the drilling and lifting once, and complete two more mixings, completing a total of "four mixing and two spraying" operations to ensure the uniformity of cement soil; the cement slurry injection pressure is 1-5MPa, and the cement content is ≥12%. For example, calculated based on the volume of the pile, ≥180kg of cement is added per cubic meter of soil to meet the strength requirements of the composite foundation pile.

[0033] The cement-soil mixing pile 2 formed by vertical continuous mixing has uniformity that meets the requirements of wind turbine foundation for pile foundation stiffness, can block the high penetration pressure of groundwater, and avoid the risk of hole collapse in traditional drilling technology. When the cement content is above 12%, the cement and sand react with hydration to form cementitious substances such as ettringite and CSH gel, which cement the loose sand particles into a whole and effectively enhance the stability of the soil around the pile.

[0034] By adopting a layered mixing process combined with pile pressing within 6 hours of the initial setting period, the construction period of a single pile can be shortened from 2 days for traditional bored piles to 1 day, significantly shortening the construction period. The 12% cement content saves cement usage compared to bored piles, and the material cost of a single pile is reduced.

[0035] Optionally, the slurry density of the thin slurry is between 1.2-1.4 g / cm³, and the spraying amount accounts for 10%-30% of the total slurry volume; the slurry density of the thick slurry is between 1.5-1.8 g / cm³, and the spraying amount accounts for 70%-90% of the total slurry volume.

[0036] In this embodiment, the cement-soil mixing pile 2 forms a whole with the prestressed pipe pile 1 after solidification, and a concrete cushion layer 3 is set on the top of the cement-soil mixing pile 2. For example, the concrete cushion layer 3 has a thickness of 100-150 mm. As a transition layer on the top of the pile, the concentrated load of the pipe pile can be dispersed to the pedestal, so that the uniformity of the compressive stress distribution on the bottom surface of the pedestal is improved; a water-stop steel plate with a thickness of 3-5 mm can be buried in the cushion layer and welded to the reserved steel bars on the top of the pipe pile to form a closed waterproof system, thereby reducing the groundwater leakage rate.

[0037] It should be noted that the cushion layer construction must be carried out after the cement soil has initially set, the pipe piles have been pressed in, and the pile top elevation has been adjusted to the design value.

[0038] With this arrangement, the cement-soil mixing pile 2 forms a whole with the prestressed pipe pile 1 after solidification, so that the bonding strength between the prestressed pipe pile 1 and the cement-soil mixing pile 2 is improved, which can withstand horizontal shear force, effectively resist the horizontal wind load of the wind turbine foundation, and avoid the foundation tilting caused by contact surface slippage.

[0039] In this embodiment, after step S300, it also includes: performing low-strain and high-strain tests and static load tests on the prestressed pipe piles 1 after being pressed in, using low-strain to detect the integrity of the pile body of all piles, and the pile body integrity should reach Class I or Class II piles, using high strain to detect the vertical compressive bearing capacity of a single pile, and testing 5 piles at each machine position, and using static load tests to detect the pull-out resistance and horizontal bearing capacity of the piles, and the number of static load tests is 3, to ensure that the pile body quality and bearing capacity of the pipe piles meet the design requirements and avoid the risk of wind turbine foundation tilting due to pile body defects.

[0040] It should be noted that the classification of pile body integrity is mainly based on the "Technical Specifications for Testing of Building Foundation Piles". Through low-strain detection (reflection wave method), the stress wave propagation characteristics of the pile body are analyzed to judge the continuity and integrity of the pile body structure. It is specifically divided into four categories: I, II, III, and IV. Among them, Class I and Class II piles are qualified piles, and Class III and Class IV piles need to be handled or judged as unqualified according to the situation; specifically, Class I piles have complete pile bodies, no defects, and meet the design bearing capacity requirements. Class II piles have slight defects in the pile body, but they do not affect the normal performance of the bearing capacity of the pile body structure.

[0041] In this embodiment, before step S100, the conditions of the foundation soil are also determined, such as a standard penetration test before construction, the sand density N value, and cement slurries with different water-cement ratios for sand layers with different densities. The higher the density of the sand layer, the smaller the water-cement ratio, so as to ensure that the sand layer does not segregate too quickly after mixing. The standard penetration test is an existing technology, and the specific operation process is not the focus of this article and will not be repeated here.

[0042] Through standard penetration tests before construction and targeted parameter and process adjustments, it can fully adapt to the complex characteristics of high groundwater and dense sandy soil strata, provide solid guarantees for the construction quality of subsequent cement-soil mixing piles 2 and prestressed pipe piles 1, and ensure the safety and reliability of the entire pile foundation project.

[0043] Preferably, a pressure sensor is provided in the hollow section of the mixer drill pipe to monitor the slurry pressure in real time with a control range of 1-5MPa. The sensor adopts a high-temperature resistant and vibration-resistant piezoresistive pressure sensor with a built-in stainless steel isolation diaphragm to resist cement slurry corrosion. 2-4 sensors are symmetrically arranged on the inner wall of the hollow section of the drill pipe 1-2m away from the drill bit. The sensors are flush with the inner wall of the drill pipe to avoid affecting the circulation of slurry; the sampling frequency is ≥100Hz, and the pressure data is transmitted to the pile driver operation panel in real time. When the pressure exceeds the range of 1-5MPa, the system automatically sounds an audible and visual alarm and adjusts the flow of the grouting pump in conjunction.

[0044] The embodiment of the present invention provides a method for constructing a wind turbine foundation pile in high groundwater and dense sandy soil, comprising the following steps: S1: Mixing pile drilling, using a single-shaft mixer to drill a hole at the designed center of prestressed pipe pile 1; S2: Mix in layers. Spray thin cement slurry when drilling for the first time. When lifting the drill, spray thick slurry while lifting the drill at a speed of 0.5-0.8m / min. Repeat the mixing for ≥2 times. The slurry mix should be controlled with a cement content ≥12%, a water-cement ratio of 0.5-0.6, and a slurry density of 1.5-1.8g / cm³. S3: Complete the pressing of prestressed pipe pile 1 within 6 hours before final setting; S4: Quality inspection. The prestressed pipe piles 1 are subjected to low-strain and high-strain inspections and static load tests after being pressed in. Low-strain inspection is used for the integrity of the pile bodies of all piles. The integrity of the pile bodies should reach Class I or Class II piles. High-strain inspection is used to inspect the vertical compressive bearing capacity of single piles. Five piles are inspected at each station. Static load tests are used to inspect the pull-out and horizontal bearing capacity of the piles. The number of static load tests is three to ensure that the pile body quality and bearing capacity of the pipe piles meet the design requirements.

[0045] Optionally, the prestressed pipe pile 1 is pressed into the pile using a hammer-driven pile-sinking method. During construction, the pile length is the main factor, and the penetration depth is secondary. If the penetration depth of the last three rounds is <30mm / 10 hits, the hammer can be stopped. If the pile cannot reach the designed elevation, the pile can be cut.

[0046] Optionally, a static pile driver is used in the pressing process of the prestressed pipe pile 1. The maximum pile driving force is determined according to the design requirements of the wind turbine foundation. A high-precision pressure sensor and a verticality monitor are equipped for the pressing construction of the prestressed pipe pile 1 to ensure the construction effect.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A wind turbine foundation pile construction method, characterized in that: The following steps are involved: constructing a cement-soil mixing pile (2) at the center of the prestressed pipe pile (1), wherein the diameter of the cement-soil mixing pile (2) is larger than the diameter of the prestressed pipe pile (1); During the construction of the cement-soil mixing pile (2), a thin slurry is sprayed when drilling for the first time, and a thick slurry is sprayed when the drill is lifted, and the mixing is repeated at least twice to form a cement-soil mixing pile (2) with a pile bottom elevation not higher than the designed bottom elevation of the prestressed pipe pile (1); Before the cement-soil mixing pile (2) solidifies, the prestressed pipe pile (1) is pressed into the designed depth.

2. A wind turbine foundation pile construction method according to claim 1, characterized in that: The method of pressing the prestressed pipe pile (1) into the designed depth comprises: The prestressed pipe pile (1) is pressed into the cement-soil mixing pile (2) by hammering or static pressure to complete the pile sinking, and the pressing force is not less than the standard value of the vertical ultimate bearing capacity of the prestressed pipe pile (1).

3. A wind turbine foundation pile construction method according to claim 1, characterized in that: The cement-soil mixing pile (2) adopts vertical continuous mixing, with a cement content of ≥12% and a water-cement ratio of 0.5-0.

6.

4. A wind turbine foundation pile construction method according to claim 1, characterized in that: The cement-soil mixing pile (2) and the prestressed pipe pile (1) are arranged concentrically, and the difference between the diameter D1 of the cement-soil mixing pile (2) and the diameter D2 of the prestressed pipe pile (1) is between 200-300 mm.

5. A wind turbine foundation pile construction method according to claim 1, characterized in that: After solidification, the cement-soil mixing pile (2) forms a whole with the prestressed pipe pile (1), and a concrete cushion layer (3) is provided on the top of the cement-soil mixing pile (2).

6. A wind turbine foundation pile construction method according to claim 1, characterized in that: Drill lifting speed ≤0.8m / min.

7. A wind turbine foundation pile construction method according to claim 1, characterized in that: The slurry density of thin slurry is 1.2-1.4g / cm³, and the spraying volume accounts for 10%-30% of the total slurry volume; the slurry density of thick slurry is between 1.5-1.8g / cm³, and the spraying volume accounts for 70%-90% of the total slurry volume.

8. A wind turbine foundation pile construction method according to claim 1, characterized in that: Also includes: After being pressed in, the prestressed pipe piles (1) are subjected to low strain, high strain testing and static load testing. Low strain testing is used for all piles to detect the integrity of the pile body. The integrity of the pile body should reach Class I or Class II piles. High strain testing is used to detect the vertical compressive bearing capacity of a single pile. Five piles are tested at each station. Static load testing is used to detect the pull-out and horizontal bearing capacity of the piles. The number of static load tests is three, ensuring that the pile body quality and bearing capacity of the pipe piles meet the design requirements.

9. A wind turbine foundation pile construction method according to claim 1, characterized in that: Before constructing the cement-soil mixing pile (2) at the center position of the prestressed pipe pile (1), the method includes: Determine the geological conditions for the pile foundation.

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